In a motor having a worm and gear, there is a need to prevent the worm and gear from reaching a back driven condition in the event that an external torque is applied at an output end of a gear arrangement. When such a motor is coupled to a load, a driving torque will act on the motor output drive under certain conditions. This torque can be transmitted from the drive gear to the worm shaft inducing an angular motion on the motor armature (back drive). When this condition is reached, the system ceases to operate as intended; for example, in the case of a window lift motor, this can mean that the window moves downward from an original position without operator intervention under vibration conditions (driving the vehicle). Another scenario causing back drive could be an individual pushing down the glass to gain access to the vehicle.
Currently, controlling a back drive condition is achieved by decreasing the gearing efficiency. However, this results in a negative effect in that the overall system efficiency is decreased as well, possibly requiring a larger motor.
By selectively having the ability to lock the drive system, the efficiency of the worm and gear arrangement can be increased to a higher level, minimizing concerns of back drive.
Thus, there is a need for a bi-directional clutch assembly for electric motors that engages whenever an output shaft side becomes the driving element thereby minimizing back drive.